Shoal-less: Backstabbing fish sacrifice pals to predators in order to save themselves, Salford uni discover

By Marios Papaloizou

The ruthless and ‘backstabbing’ behaviour of fish has been observed for the first time by experts from Salford University.

The bizarre behaviour saw shoals of fish turning on their own weak members to injure and leave behind for a looming predator to gobble up. 

The cut-throat phenomenon – of fish literally ‘selling each other down the river’ – was first observed by Professor Robert Young from the University of Salford’s school of Environment and Life Sciences.

On a trip to Brazil Professor Young noticed that, when threatened, shoals of two-spot astynax would bite and ram weak members leaving them stunned and as easy meat for a predator.

After investigating further it was concluded that the behaviour only occurs during a situation where one fish will be targeted by a predator for attack.

 “This hasn’t been observed before, possibly because most social animals tend to punish members of the group which break rules,” Professor Young said.

“However, in the case of the astynax, treachery appears to be tolerated and all of the members of the group are happy enough to join in.

“It’s rough luck for the victim, but in the wild in helps ensure that the more ruthless members of the shoal can stay alive and breed.”

SELF-FISH: The Brazilian astynax will attack weak members to leave them behind

The behaviour has never been seen before and Professor Young believes that it is because of the small sizes of the shoals.

 “In an attack each of the fish has a one in eight chance of being attacked, so this behaviour helps with the odds,” he said.#

Top picture courtesy of Mattk1979, with thanks.

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